The present invention relates generally to a hand held printer which prints both characters and drawings on a print paper in response to manual movement of the printer over the surface of the print paper, and more particularly to a hand held printer which incorporates an input unit, a display unit, a character storage unit and a printing device in a single housing.
In order to understand the background of the invention, reference is first made to FIG. 1 wherein a conventional hand held printer, generally indicated at 100, for printing on a print paper through manual movement over the paper, is depicted. Because of the manual operation of such hand held printers, the plurality of motors usually required to drive a normal carriage contained printer and the control circuits for controlling those motors are not needed thereby allowing for greater miniaturization and portability. However, to control the printing, the conventional hand held printer has to be connected to a large host unit 75 through interface cables 74A and 74B. Printer 100 has a manually movable body 70 movable over a print surface 106 which contains a position detector 72 which is rotated by a roller 69 when body 70 is manually moved over print surface 160. An encoder 73 detects the motion of position detector 72 and produces signals which are detected by host unit 75. Host unit 75 detects the pulse signals from encoder 73 and a control unit within host unit 75 outputs a pattern of characters and drawings to a print head 71 in response to the pulse signals from encoder 73 in order to print on surface 160 as printer body 70 is moved thereover. In such an apparatus, the pattern of the characters and drawings to be printed by print head 71 are input using a separate input unit 76, a separate display unit 77 and a separate storage unit in host unit 75. Such a conventional printer is disclosed in U.S. Pat. No. 3,767,020 issued Oct. 23, 1973 to Rowe.
Conventional hand held printers are known in the art as illustrated by Japanese Laid Open Patent Nos. 60-109866, 62-244683 and 61-283574 and Japanese Laid Open Utility No. 61-16685. In these conventional hand held printers, a thermal ink ribbon is sandwiched between a fixed roller and the print surface. The ink ribbon is moved by the manual movement of the hand held printer over the print paper. Printing may also be accomplished by pressing the printer on the paper and manually moving the printer to perform the printing.
Additionally, many hand held lettering tape printing devices have also been proposed. These require a motor for driving the roller which draws out the ink ribbon and the lettering tape as well as motors for controlling the ink ribbon take up reel. Additionally, a control circuit for controlling the motor is required resulting in a large sized apparatus. Accordingly, printing is possible only on special lettering tapes.
These hand held printers have been less than satisfactory. It is impossible to use the conventional hand held printer without the associated input unit, display unit, storage unit and control unit of a host unit. Accordingly, even if the hand held printer is small and portable the apparatus itself is not portable due to the large sized associated control units. Additionally, the structure of the prior art hand held rollers results in unstable application of pressure by the thermal head and the roller on the ink ribbon during manual operation. Accordingly, only the pressure of the thermal head acts on the ribbon and the pressure applied on the ribbon by the printing surface of the roller is either very small or non-existent. When this occurs, the roller cannot rotate and it becomes impossible to feed and take up the thermal ink ribbon. The thermal ink ribbon runs out from the printer causing undesirable staining of the print surface making a usable print operation impossible. Furthermore, the print roller slips due to the interlocking the thermal ink ribbon during operation. When the roller does slip, it falls out of sync with the signal sent by the encoder corresponding to the displacement of the hand held portion of the printer across the surface. Because the host unit no longer has accurate data as to the distance moved by the hand held printer, the characters or drawings are printed out of sync with the actual displacement of the printer resulting in misformed printed symbols.
The roller also acts as the ink ribbon take up roller for the used up thermal ink ribbon. The roller relies on the driving forces generated by the friction of the roller engaged with the print surface when the roller presses the ink ribbon onto the printing paper during operation. This requires that a large downward force be applied to the printer to obtain an adequate friction and driving force to take up the thermal ink ribbon. When such a force cannot be provided, the ribbon is not taken up by the roller, resulting in the thermal ink ribbon running out from the printer causing major defects in the printed symbol such as staining of the printed surface making operation of the printer impossible. On the other hand, when large forces are applied to the hand roller they tend to damage the hand held printer due to deterioration of parts due to the operation under high pressures, forces and stresses
Additionally, the conventional hand held printers do not contain a ribbon guide member for guiding the travel direction of the thermal ink ribbon through the printer during printing. This results in displacement, loosening, jamming and the projecting of the ink ribbon from the thermal head during operation causing deterioration of print quality and deterioration in the maintainence of print consistency during operation. Such conventional hand held printers which do include a ribbon guide still result in handling problems of the travelling surface resulting in poor operation, detachment of the ribbon when the ribbon cassette is detached from the hand held printer and related problems Additionally, due to the gap between the thermal head and the print surface or inconsistencies in the print surface, the thermal ink ribbon and thermal print head do not closely adhere to the printing surface causing misprinting of the symbols to create light and dark areas.
Accordingly, it is desired to provide an improved hand held printer which overcomes the shortcomings of the prior art and which achieves the objects and benefits associated with a completely portable, manually activated printer